Hello,
According to instructions we received from TAC some time ago, the downgrade with deployment policy is not supported, you will need to send push operations to uninstall the agent, probably delete the machines from your server and install again. In our case, when tried to downgrade, most of the endpoints downloaded the new package but installation failed, in some few cases, downgrade caused very strange problems on the machine and had to re install drivers or even the entire OS, so i would not recommend it at all (with deployment rules). I do not know your scenario/problem, but if you are hitting some kind of bug or error with the agent i would try a newer version, it worked for us several times.
Regards